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Update on SPS BPM impedance

Update on SPS BPM impedance

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Update on SPS BPM impedance

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  1. Update on SPS BPM impedance B. Salvant for the 2008 impedance team

  2. Reference: http://cdsweb.cern.ch/record/1208424/files/CERN-ATS-2009-046.pdf • 106 BPH and 96 BPV in the SPS • Low frequency imaginary impedance for a BPH :Zlong/n ~ 1 mΩ, Zx=- 0.1 kΩ/m and Zy=2 kΩ/m. • Separate simulations for a BPV: Zlong/n~0.5mΩ, Zy= 0.1 kΩ/m and Zx= 0.2 kΩ/m.

  3. Modelled structure for the BPH Ultrarelativistic beams All materials are perfect conductors (except the ceramic spacers) In fact: - Electrodes + pipe should be inStainless Steel - Casing should be in Anticorodal Rs=|V|^2/Plosses

  4. BPH longitudinal (with material losses)

  5. BPH vertical (with material losses)

  6. BPH horizontal (with material losses) Quite insignificant change of transverse displacement on shunt impedance

  7. BPV

  8. From PhD thesis…

  9. BPV (with material losses) Longitudinal vertical horizontal

  10. Effect on the beam Headtail simulations • Simulations done at the time with small longitudinal emittance (0.15 eVs) • All BPMs are lumped in one location accounting for the respective beta functions. • Linear longitudinal restoring force • No direct space charge

  11. BPMs alone (vertical plane)

  12. BPMs alone (horizontal plane)

  13. Summary • Effect of impedance of BPH and BPV is small on transverse single bunch dynamics • Longitudinal modes : • Rs~1 to 10 k Ω • R/Q~ 5 to 20 Ω • Larger for BPHs than BPVs • Frequencies above 1 GHz • Transverse modes: • Modes at 0.5 GHz (vertical for BPH) and 0.7 GHz (horizontal for BPV) • Rs~1 to 20 kΩ/m • R/Q~ 5 to 50 Ω/m

  14. However… ?

  15. Effect of matching the impedance at electrodes coaxial ports in Particle Studio simulations (BPH) Modes are damped by the “perfect matching layer” at the coaxial port Short bunch (1 cm rms) SPS bunch (20 cm rms) Electrodecoaxial port Importance to match the BPM electrodes!

  16. BPH Longitudinal vertical horizontal

  17. Longitudinal Time domain (CST PS) Frequency domain eigenmode solver at the peaks (CST MWS)

  18. Dipolar vertical impedance (PEC)

  19. Longitudinal (with losses) Electrodes + pipe  Stainless Steel Casing  Anticorodal